3 months pregnant with a vague pain in the stomach is due to physiological reasons, miscarriage and acute gastroenteritis and other reasons. 1. Physiological reasons: 3 months pregnant due to the enlarged uterus has protruded from the pelvis, will have a certain pulling effect on the surrounding tissues, ligaments, will cause vague pain in the stomach, usually after appropriate rest will be relieved, is a normal physiological phenomenon. 2. Pre-eclampsia: when the stomach aches in the third month of pregnancy, there may be symptoms of pre-eclampsia, accompanied by a small amount of vaginal bleeding, ultrasound suggests that the development of the fetus is normal, according to the clinical manifestations and progesterone tests can assist in the diagnosis, and need to comply with the doctor’s instructions to protect the fetus treatment. 3. Acute gastroenteritis: can also cause vague pain in the stomach, can also be accompanied by diarrhea, fever and other symptoms, there is a history of improper diet or unclean diet, combined with the history and clinical manifestations can be diagnosed. During pregnancy, pay attention to rest, at the same time should relax, avoid tension, anxiety, any discomfort should be timely to the hospital, the doctor to clarify the diagnosis, and cooperate with the doctor to deal with the symptoms.